You obviously already know "Präserviertes Gemüse" is (Very uncommon) German and translates into "preserved vegetables".

I haven't seen any tinned food around here (In Germany) - and i kind of live on it 8-/ - wich was labeled as "präserviert". "Präserviert" associates with "Präservativ" (A German word for Condoms) and i guess any marketing person suggesting to label food with it would be shot at once...

So this is either due to some translation error, an intra-chinese marketing trick to suggest "German quality" to chinese buyers or a very very very old tin from a time when people didn't talk about such things as condoms. Maybe from before the war. The first WW... 8-)